U.S. Pat. No. 5,076,299 and No. 5,033,487 disclose a hair curler A1, which is heated by a heater and enables a hair curling to be easily performed with the hair curlers A1 and without any chemical agent. The hair curler A1 has a hollow heat-receiving cylinder A2 and a wrapping shell A3 extending outward from the flange of A2's end. The current heater device for hair curlers A1 is shown in FIG. 1 PRIOR ART. An upper hood and a lower casing form a disposing space for hair curlers A1. A disposing seat, which has multiple heating cylinders of the same number as the hair curlers, is installed inside the disposing space. A heater part coupled to an external power source is attached to the bottom of the disposing seat. The heater part comprises: an electrothermal plate B1; a heat-conducting plate B2, which is attached to the disposing seat and the electrothermal plate B1 and contacts the bottom ends of the heater cylinders; and a fixing plate B3 attached to the bottom of the electrothermal plate B1. When undertaking hair curling, the user hoods the heat-receiving cylinder A2 of the hair curler A1 over the heating cylinder. The heat created by the electrothermal plate B1 is spread by the heat-conducting plate B2 and conducted upward to the heating cylinders via the contact between the heat-conducting plate B2 and the bottom ends of the heating cylinders. Thus, the heat-receiving cylinders A2 of the hair curlers A1 neighboring the heating cylinders are heated and accumulate energy. Then, the user takes out the heated hair curlers A1 and winds hair over the heat-receiving cylinders A2 and uses the wrapping shells A3 to confine the hair. Thus, the heat accumulated inside heat-receiving cylinders A2 can make the hair curled for a period of time.
In the conventional technology described above, the heat created by the electrothermal plate B1 is transmitted through the heat-conducting plate B2 to the heating cylinders; however, there is only a ring-type contact between the heat-conducting plate B2 and the heating cylinder; therefore, the heat conduction speed is pretty low, and there is a temperature difference between the top and the bottom of the heating cylinder, and the heat cannot be uniformly accumulated from the top to the bottom of the heat-receiving cylinders A2 of the hair curlers A1. Thus, the curling extent of the hair wound over the same heat-receiving cylinders A2 will vary, and the hair curling effect will be influenced.